1. Field of the Invention
The present invention relates to brake devices having a pump that serves to pump a working liquid previously discharged into a reservoir from the wheel cylinders and to deliver the working liquid to a master cylinder via a discharge valve associated with the pump.
2. Description of the Related Art
In general, brake devices have a master cylinder and a wheel cylinder(s). The master cylinder serves to pressurize a working liquid in response to the operation of a brake pedal so as to deliver hydraulic pressure via the working liquid to the wheel cylinder(s). The wheel cylinder(s) then functions to press the friction surfaces of brake pads against a brake disk as a result of the pressure of the working liquid.
Brake devices having an anti-lock function for preventing a wheel(s) from being locked up during braking (i.e., stopping rotation while the vehicle is still moving) are also known. These types of brake devices typically have an actuator that includes a reservoir and a pump. The reservoir serves to store the working liquid that is discharged from the wheel cylinder(s) when the pressure of the wheel cylinder(s) is to be reduced (thereby, eliminating or preventing the locking effect upon the wheel). The pump then serves to pump the working liquid stored within the reservoir in order to deliver the working liquid to the master cylinder. Conventionally, a reciprocating pump (e.g., a plunger pump) has been generally used as a pump for this type of brake device. Japanese Laid-Open Patent Publication No. 8-230642 and U.S. Pat. No. 6,000,764 teach such brake devices.
However, the working liquid discharged from the reciprocating pump naturally has pulsations in pressure. Such pulsations may cause vibrations of various pipelines, the master cylinder, etc., of the brake device, possibly producing unpleasant vibration sounds. In addition, vibrations may be transmitted to the vehicle body and create an uncomfortable feeling or sensation for passengers.
In order to reduce the effects of pulsations of the working liquid, there has been proposed to provide a damper chamber on the downstream side of the pump. However, in many cases it has been difficult to effectively suppress the pulsations only by the provision of the damper chamber.